This invention relates to a method for surveying actual measurement data of a component and an apparatus for performing such method.
The method and the apparatus of the invention can in particular be used for checking components. For checking components, various methods are known already.
In a conventional and widely used method for surveying, inspecting and checking components, a physical component is examined by means of a coordinate measuring instrument, wherein this examination mostly is performed automatically. The physical component is probed in a tactile way by a measuring stylus, the actual measurement data are obtained, and the deviations from the scheduled data are detected. Such tactile measuring instruments are widely used in particular in the industry. When surveying a component with a tactile coordinate measuring instrument, which can also be referred to as coordinate measuring machine, only few interesting measurement points of the surface of the component or of the object to be examined usually are approached and the corresponding measurement data are obtained, for instance a hole diameter or a hole position, certain functional dimensions, certain distances and the like. Since the tactile survey is relatively time-consuming, it is common practice not to survey or scan the entire component or object, but only those parts or individual dimensions of the component which are of particular interest.
Another known method consists in optically surveying a component. According to this method, the component is optically scanned, in particular by means of an optical scanner. In the optical measurement technique, the “entire surface” of the component usually is scanned and recorded. As a result, actual measurement data of the component are obtained. The data record of the actual measurement data forms a virtual image of the physical component in the form of its surface points, wherein the surface points usually are recorded as 3D coordinates. This data record of the actual measurement data, i.e. the virtual component, can be visualized on a screen. Furthermore, the data record of the actual measurement data can be processed or edited. By means of special evaluation software, so-called inspection software, the actual measurement data can be surveyed. As a result, certain dimensions of the virtual component can be determined. These dimensions are based on the actual measurement data, from which the virtual component is formed. They can be compared with the scheduled data of the respective dimension. In this way, all dimensions which can be “scanned” in a tactile way on the physical component can equally be determined from the data record of the actual measurement data by suitable algorithms. At present, components increasingly are also surveyed with an optical measurement technique, since the optical measurement technique meanwhile has gained ground in terms of measurement accuracy with respect to the tactile measurement technique and a 100% examination of a component can also be effected with the optical measurement technique. With the optical measurement technique a full-surface comparison of the component can also be performed. Furthermore, the optical measurement technique involves reduced measurement times.
The apparatuses and systems for the optical scanning of surfaces, which are available on the market, are based on the principle of the pure measurement of coordinates. This means that mostly point aggregates are measured. These point aggregates can be thinned out, filtered and cross-linked in a subsequent process, in order to reduce the amount of points (mostly several millions), wherein the information content is not or only slightly reduced. By using a computer and an inspection software, an inspection can then be performed on the basis of this data record. For this inspection, certain dimensions are determined from the data record of the actual measurement values, which are compared with the associated scheduled data.
From DE 199 25 462 C1, there is known a method for surveying actual measurement data of a component, which originate from an optical scan. In this method, measurement marks are applied on a three-dimensional body. In a data processing unit, a 3D scheduled data record of the surface of the three-dimensional body is stored. Between the stored scheduled data and the measured actual data a variance comparison is performed. The surface reference points defined in the 3D scheduled data record are transferred to the three-dimensional body, wherein these transferred reference points then represent specified positions for applying the measurement marks.
DE 43 20 485 discloses a method for surveying objects by means of a distance image camera.
From DE 10 2004 061 338 A1 a method for testing a component is known, in which the component is examined by means of a testing sensor, whose position is detected.